Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured with small size and weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
For the middle- or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle- or large-sized battery module to be constructed in a structure in which a plurality of battery cells are electrically connected in series with each other, and the battery cells are stable against an external force.
Also, the battery cells constituting the middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary battery during the charge and discharge of the battery cells. If the heat, generated from the unit cells during the charge and discharge of the unit cells, is not effectively removed, the heat accumulates in the respective unit cells, with the result that the deterioration of the unit cells is accelerated. According to circumstances, the unit cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
In a middle- or large-sized battery pack including a plurality of battery cells, on the other hand, the deterioration in performance of some battery cells leads to the deterioration in performance of the entire battery pack. One of the main factors causing the nonuniformity of the performance is the nonuniformity of cooling between the battery cells. For this reason, it is required to provide a structure to secure the uniformity of cooling during the flow of a coolant.
Generally, when designing a middle- or large-sized battery pack constructed in a structure in which a duct at a coolant inlet port side (hereinafter, referred as an ‘inlet duct’) and a duct at a coolant outlet port side (hereinafter, referred as an ‘outlet duct’) are arranged horizontally, it is difficult to achieve uniform distribution of coolant flux between a plurality of battery cells. Especially, the coolant flux concentrates between the battery cells disposed adjacent to the coolant inlet port, with the result that the battery cells disposed adjacent to the coolant inlet port are excessively cooled, whereas the temperatures of the cells disposed distant from the coolant inlet port relatively increase. As a result, the temperature difference between the battery cells increases, with the result that the overall performance of the battery pack lowers due to the deterioration of the battery cells.
On the other hand, it is possible to change the shape of the inlet duct and the outlet duct in order to solve the above problems. In this case, however, the size of the battery pack may increase, and the structural stability of the battery pack may lower, due to the change in shape of the inlet duct and the outlet duct. For this reason, it is preferred to solve the above deterioration-related problem without changing the shape of inlet duct and the outlet duct.
As a technology for solving the problems caused due to the nonuniform distribution of the coolant, Korean Patent Application Publication No. 2006-037601 discloses a battery module including a plurality of unit cells arranged at predetermined intervals and a housing in which the unit cells are mounted, wherein the housing has an inlet part to introduce air for temperature control in a direction inclined to the direction in which the unit cells are arranged and an outlet part to discharge the air having passed through the unit cells. In the disclosed battery module, however, the housing at the inlet part is inclined, with the result that it is difficult to install the battery module in an external device, such as a vehicle. Furthermore, an additional guide member is not mounted in the inlet part, with the result that it is not possible to accurately control the flux of a coolant flowing between the respective battery cells.
Consequently, there is a high necessity for a technology to fundamentally solve the above-mentioned problems.